The present application relates to an illumination apparatus including a light transmission film on a surface of which three-dimensional structures are continuously arranged, and a liquid crystal display apparatus.
A liquid crystal display (LCD) apparatus can realize lower power consumption and reduction in size and thickness as compared to a cathode ray tube (CRT), and thus is currently widely used for a large-size LCD television, compact apparatuses such as a mobile phone, a digital camera, and a personal digital assistant (PDA), and like other products of various sizes.
The liquid crystal display apparatuses are categorized into, for example, a transmission type and a reflection type. In particular, the transmission-type liquid crystal display apparatus includes a liquid crystal display panel, a light-incident-side polarization plate, a light-exit-side polarization plate, and a backlight unit as an illumination light source. The liquid crystal display panel is formed by sandwiching a liquid crystal layer by a pair of transparent substrates. The light-incident-side polarization plate and the light-exit-side polarization plate are disposed on a light incident side and a light exit side of the liquid crystal display panel, respectively. The backlight units are categorized into a direct type backlight and an edge-light type backlight. The direct-type backlight unit has a light source disposed right below the liquid crystal display panel. The edge-light type backlight unit uses a light guide plate.
On the other hand, there has been known a structure in which a light transmission film referred to as a prism sheet is disposed between the backlight unit and the liquid crystal display panel in order to distribute outgoing light from the liquid crystal display panel so that the light has a larger intensity toward the front. The prism sheet includes a prism portion formed by arranging a plurality of structures, each of which has an approximately triangular cross section and has a ridge line in a first direction (ridge line direction), in a second direction (arrangement direction) perpendicular to the first direction. The prism sheet exhibits an operation of improving front luminance by causing light from the backlight unit to travel toward the front.
In addition, it has been proposed that the front luminance and a use efficiency are further improved by imparting refractive index anisotropy to the prism sheet including prisms each having an approximately triangular cross section (see, WO2007/032440). According to WO2007/032440, the refractive index of the prism in the ridge line direction is set to be larger than that in the arrangement direction. As a result, out of light that enters the light transmission film, polarization components oscillating in the ridge line direction more than those oscillating in the arrangement direction become return light. Accordingly, a certain polarization separation function can be obtained. Thus, a transmission axis of the polarization plate is aligned in the arrangement direction of the prism having a small refractive index, which can improve the front luminance.